I been using 20 to 1 in my 16 to 1 and 25 to 1 motors – I don’t have to keep yet another can of gas mixed, and it’s convenient to dump a quart of oil in a 5 gallon can. I also keep cans mixed at 8 to 1 for my PO-15 Johnson, and 50 to 1 for 50 to 1 and 100 to 1 motors. I use generic TCW3 oil.
One exception – whatever motor I put on my grandson’s hydroplane (6 to 15 HP depending on who’s running it) I double whatever the manufacturer recommends because these motors are revving higher RPMs than designed for. Note I do not have any special racing models. On the hydroplane, I go one heat range colder on the spark plugs.